The invention relates to a valve control for internal combustion engines, comprising a hydraulic arrangement located between the camshaft and the valve. The arrangement varying, by way of a piston system mounted in a housing, the valve stroke and opening time in response to different operating conditions of the internal combustion engine.
The power, torque, exhaust gas emission, and fuel consumption of an internal combustion engine can be optimized by varying the stroke and control time of a valve control. Under full load, maximum stroke and maximum opening time are necessary for this purpose, while in the partial load range these two valve control quantities must be reduced.
In a known valve control (periodical Road and Track, April 1977, page 122) an axially movable camshaft carrying a sloping cam cooperates with a valve. The valve stroke and opening time vary in dependence of the cam axial position. The variation is determined in response to the rpm by a centrifugal governor. This structure entails the disadvantage that highly abrasive friction forces develop in the variation determining the shifting process between the camshaft and the shaft end penetrating therein. In addition the elements of this shifting arrangement provide for mechanical complication resulting in high costs.
To avoid these problems a hydraulic arrangement comprising a piston system is arranged between the camshaft and the valve in a known valve control (German Offenlegungsschrift-No. 2,101,542). The stroke and control time variation occurs in response to the oil pressure in the internal combustion engine. It has been found disadvantageous in this case that the oil pressure increase and decrease over the rpm range is not constant, which interferes with exact variations. The oil viscosity and temperature also may cause irregularities.
Furthermore, especially in the engine partial load range, the valve always strikes hard on its seat since in this operating condition the valve leads the cam.
Therefore, an object of the present invention is to provide, between the camshaft and the valve of an internal combustion engine, a hydraulic arrangement designed to vary the valve stroke and control time, and adapted functionally and exactly to changing engine operating conditions. Provisions are made also to avoid the hard impact of the valve on its seat on closing, especially in the partial load range.
According to the present invention this object is achieved by a hydraulic arrangement interposed between the cam shaft and valve which has a piston system with at least a power piston and an actuating piston, the piston system being influenced by a throttle element that is controlled in response to one or more engine operation parameters. In one embodiment the piston system has at least three pistons, a drive piston being interposed between the power and actuation pistons, and in all cases a damping means is provided for controlling the valve seating operation.
The primary advantages derived from the invention result from the provision of a piston system comprising at least three pistons, the damping means, and the throttle element responsive to engine parameters determining the satisfactory operation of the hydraulic arrangement varying the valve stroke and opening time. The damping means provides for the deceleration of the valve and the damping of the end of the seating action, especially in the partial load range.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.